HR: 0830h
AN: A31D-0064    [PDF]
TI: Negative Ion Chemical Ionization Mass Spectrometric Technique for the Detection of Atmospheric Molecular Halogens
AU: * Keil, A D
EM: keilad@purdue.edu
AF: Department of Chemistry, Purdue University, 560 Oval Drive, Lafayette, IN 47907-2084 United States
AU: Shepson, P B
EM: pshepson@purdue.edu
AF: Department of Chemistry, Purdue University, 560 Oval Drive, Lafayette, IN 47907-2084 United States
AB: As a greenhouse gas and regulated pollutant, tropospheric ozone not only impacts regional air quality but also global climate. At the same time, it is essential as it determines, in part, the oxidizing capacity of the atmosphere. In light of this, understanding ozone depletion events that occur over the Arctic Ocean and in the marine boundary layer is important in predicting the future state of the atmosphere. Halogen chemistry is thought to play an important role in these ozone destruction events, but the sources and reservoirs of halogen atoms are not well understood. Molecular halogens (Cl$_{2}$, Br$_{2}$, and BrCl) have been identified as potentially important photolytic precursors to halogen atoms, but instrumentation for their detection has thus far precluded routine study and understanding of the production of the molecular halogens in the Arctic. The development of a negative ion chemical ionization mass spectrometric technique for the detection of ambient molecular halogens will be discussed. The technique uses electron impact of nitromethane to produce NO$_{2}$$^{-}$, which through an electron transfer ion molecule reaction in a quardropole ion trap, produces the molecular anion of the corresponding molecular halogen. The rate constant of the reaction Br$_{2}$ + NO$_{2}$$^{-}$ (relative to the published rate constant of Cl$_{2}$ + NO$_{2}$$^{-}$) was determined to be 1.4$\pm$0.4*10$^{-9}$ cm$^{3}$/molecule-s. Sample introduction into the mass spectrometer, standardization methods, and preconcentration techniques will also be discussed.
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting